1. Field of the Invention
The present invention relates to single crystal material modulators/deflectors which utilize a MgF.sub.2 layer to promote both the adherence of a piezoelectric transducer and antireflection coatings to the material.
2. Description of the Prior Art
A typical prior art single crystal material modulator/deflector comprises a lithium niobate transducer bonded to one surface of the underlying material through an intermediate thin film layer, such as indium. The crystal material is, on the surface exposed to the incident light beam, provided with an antireflection coating, such as thorium fluoride. This prior art configuration is described in U.S. Pat. No. 3,617,931. An article by G. J. Zydzik et al., Applied Physics Letters, Vol. 31, No. 10, Nov. 15, 1977, describes the use of fluoride thin films to bond vacuum-evaporated gold onto oxide or glass substrates.
Experiments have indicated that when vacuum deposited SiO.sub.2 is utilized as the anti-reflection coating or chrome is used as the intermediate bonding layer, these materials would not repeatably adhere to the underlying single crystal material (such as TeO.sub.2) and could be easily removed. SiO.sub.2 is difficult to apply to the single crystal material due to temperature coefficient differentials between SiO.sub.2 and the crystal material.
What would be desirable therefore is to provide an improved bonding technique which would substantially enhance the bonding capability of a piezoelectric transducer to a single crystal structure and which substantially enhances the adhesion of anti-reflection coatings to the single crystal structure in a manner such that the coatings are durable and can be cleaned without substantial peeling or scratching.